Frequency domain spectroscopy (FDS) measurement has become an important method for the assessment of the condition of the insulation of oil transformers. In recent years, numerous researchers have found that temperature variation affect FDS results. The master curve technique is commonly used to correct the effect of temperature on FDS results. In this paper, an FDS experiment is carried out on a sample transformer. Then, for this transformer, insulation model parameters are determined by using a genetic algorithm based on the FDS results. Then, by using the insulation model parameters, tanδ curves are simulated and compared to real results. Finally, an FDS experiment is conducted on two other transformers at 22 °C, 30 °C, 40 °C, 50 °C, 60 °C, and 70 °C (in order to give sufficient information for a training neural network) and insulation model parameters are calculated via the genetic algorithm. In one of the transformers, the effect of temperature on the FDS curves is corrected by using the master curve technique and the FDS curves are transmitted over the reference curve. It is also shown that the transformer insulation is an Arrhenius-type dielectric. The error of this method is calculated by using a mean square error technique. In the two other transformers, the insulation model parameters related to 22 °C are considered as the target parameters. The insulation model parameters of the other temperatures are fed into an artificial neural network as input, to train it to transfer insulation model parameters related to other temperatures to the reference parameters. Finally, the errors of both methods are compared, and it is shown that this latter method for correcting the temperature effects in the FDS method is the more effective.
PurposeThe purpose of this paper is to study very fast transient overvoltages (VFTOs) in the secondary winding of air‐cored Tesla transformers and also study the resulting electric field stresses.Design/methodology/approachAn exhaustive model based on Multi‐conductor Transmission Lines (MTLs) theory has been used. The governing telegraphist's equations have been solved by Finite Difference Time Domain (FDTD) method.FindingsThe results demonstrated that there are some overvoltages at the end and middle turns that should be considered in insulation design. The magnitudes of these overvoltages are several times more than the steady state value of the corresponding turn which cause very high electric field stresses.Originality/valueThe paper describes results obtained from an original and innovative implementation of FDTD method in transmission line modelling and is applied properly to air‐cored pulse transformers.
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